I'd like to understand this in as precise a detail as possible.
Is there a list of Union states were slave states during the Civil War.
Border states of the slaves states of Delaware, Kentucky, Maryland, Missouri, and West Virginia are interesting as their internal violence regarding slavery was offset by what happened if border slave states seceded as well.
Border states of the slaves states of Delaware, Kentucky, Maryland, Missouri, and West Virginia
Delaware, Kentucky, Maryland, Missouri and West Virginia were Union States and were never part of the Confederacy. They were Union states that had legal slavery. That is a slave state. NJ was a slave state. NY was a border state of a slave state.
At all times since the District of Columbia was created, it has been under the authority of Congress. Congress could have constitutionally banished slavery in the district at any time with simple legislation, as it did in 1862.
West Virginia did not exist as a state until the end of 1863. For all of the state of Virginia, the rump government in Alexandria (not Richmond) was recognized by the U.S. Government as the official government, and this rump government approved the partitioning of the State of Virginia into two states in make believe compliance with the Constitution.
U.S. Const., Art. 4, Sec. 3: "Section 3.
New states may be admitted by the Congress into this union; but no new states shall be formed or erected within the jurisdiction of any other state; nor any state be formed by the junction of two or more states, or parts of states, without the consent of the legislatures of the states concerned as well as of the Congress."
Partitioning required the consent of the congress of the State of Virginia. After the war, in Texas v. White, Scotus found that was an indestructible union of indestructible states, and that no state had ever left the union. Officially, no state ever actually seceded.
While having a fully recognized government for the whole state in 1863, after the war Virginia needed reconstruction to form a recognized government.